System and Method for Identifying a Vascular Border

ABSTRACT

A system and method is provided for using a first vascular image, or more particularly a plurality of control points located thereon, to identify a border on a second vascular image. Embodiments of the present invention operate in accordance with an intra-vascular ultrasound (IVUS) device and a computing device electrically connected thereto. Specifically, in one embodiment of the present invention, an IVUS console is electrically connected to a computing device and adapted to acquire IVUS data. The IVUS data (or multiple sets thereof) is then provided to (or acquired by) the computing device. In one embodiment of the present invention, the computing device includes a plurality of applications operating thereon—i.e., a border-detection application, an extrapolation application, and an active-contour application. These applications are used to (i) identify a border and control points on a first IVUS image (i.e., any IVUS image), (ii) extrapolate the control points to a second IVUS image (i.e., another IVUS image), (iii) identify a border on the second IVUS image, and (iv) adjust the border on the second IVUS image in accordance with at least one factor. In one embodiment of the present invention, the at least one factor is selected from a group consisting of gradient factor, continuity factor, and curvature factor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit pursuant to 35 U.S.C. §119(e) ofU.S. Provisional Patent Application Nos. 60/406,148, 60/406,183,60/406,184, 60/406,185, 60/406,234, and 60/406,254, all of which werefiled Aug. 26, 2002, and all are incorporated herein, in their entirety,by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to vascular borders, or more particularly,to a system and method of using a first vascular image (or controlpoints located therein) to identify a border on a second vascular image.

2. Description of Related Art

The present invention relates to medical imaging arts. It findsparticular application to a system and method of, identifying a borderin an intra-vascular ultrasound (IVUS) image. It should be appreciatedthat while the present invention is described in terms of identifying aluminal and medial-adventitial border on an IVUS image, the presentinvention is not so limited. Thus, for example, identifying any border(or boundary) in any vascular image is within the spirit and scope ofthe present invention.

Ultrasonic imaging of portions of a patient's body provides a usefultool in various areas of medical practice for determining, the best typeand course of treatment. Imaging of the coronary vessels of a patient byultrasonic techniques can provide physicians with valuable information.For example, the image data may show the extent of a stenosis in apatient, reveal progression of disease, help determine whetherprocedures such as angioplasty or atherectomy are indicated or whethermore invasive procedures may be warranted.

In a typical ultrasound imaging system, an ultrasonic transducer isattached to the end of a catheter that is carefully maneuvered through apatient's body to a point of interest such as within a blood vessel. Thetransducer may be a single-element crystal or probe that is mechanicallyscanned or rotated back and forth to cover a sector over a selectedangular range. Acoustic signals are then transmitted and echoes (orbackscatter) from these acoustic signals are received. The backscatterdata can be used to identify the type or density of a scanned tissue. Asthe probe is swept through the sector, many acoustic lines are processedbuilding up a sector-shaped image of the patient. After the data iscollected, an image of the blood vessel (i.e., an IVUS image) isreconstructed using well-known techniques. This image is then visuallyanalyzed by a cardiologist to assess the vessel components and plaquecontent.

A typical analysis includes determining the size of the lumen and amountof plaque in the vessel. This is performed by generating an image of thevessel (e.g., an IVUS image) and manually drawing contoured boundarieson the image where the clinician believes the luminal and themedial-adventitial borders are located. This is a very time consumingprocess. Furthermore, this process is made more difficult when multipleimages are being analyzed (e.g., to recreate a 3D vascular image, etc.)or the images are of poor quality (e.g., making the boundaries moredifficult to see). Thus, it would advantageous to have a system andmethod of identifying a border on a vascular image that overcomes atleast one of these drawbacks.

SUMMARY OF THE INVENTION

The present invention provides a system and method of using a firstvascular image, or more particularly a plurality of control pointslocated thereon, to identify a border on a second vascular image.Embodiments of the present invention operate in accordance with anintra-vascular ultrasound (IVUS) device and a computing deviceelectrically connected thereto. Specifically, in one embodiment of thepresent invention, an IVUS console is electrically connected to acomputing device and a transducer via a catheter. The transducer isinserted into a blood vessel of a patient and used to gather IVUS data(i.e., blood-vessel data, or data that can be used to identify the shapeof a blood vessel, its density, its composition, etc.). The IVUS data isthen provided to (or acquired by) the IVUS console, where it is used toproduce an IVUS image of the vessel.

The IVUS data (or multiple sets thereof) is then provided to (oracquired by) the computing device. In one embodiment of the presentinvention, the computing device includes a plurality of applicationsoperating thereon—i.e., a border-detection application, an extrapolationapplication, and an active-contour application. These applications areused to (i) identify a border and control points on a first IVUS image(i.e., any IVUS image), (ii) extrapolate the control points to a secondIVUS image (i.e., another IVUS image), (iii) identify a border on thesecond IVUS image, and (iv) adjust the border on the second IVUS imagein accordance with at least one factor.

Specifically, the border-detection application is adapted to identify aborder on a vascular image (e.g., an IVUS image). In one embodiment ofthe present invention, this is accomplished by analyzing the IVUS image,or IVUS data that corresponds to the IVUS image, to determine certaingradients located therein. This is because borders of vascular objectscan be identified by a change in pixel color (e.g., light-to-dark,dark-to-light, shade1-to-shade2, etc). Once the border is identified,the border-detection application is used to identify at least onecontrol point (i.e., a starting-control point) on the identified border.The extrapolation application is then used to identify at least onecontrol point (i.e., an additional control point) on at least one otherIVUS image. In a preferred embodiment of the present invention, this isdone by extrapolating the previously identified control point (i.e., thestarting-control point) to at least one other IVUS image. Once thecontrol point(s) is extrapolated, the extrapolating application isadapted to identify (or approximate) a border that passes through theextrapolated point(s).

The active-contour application is then used to adjust the approximatedborder (i.e., the border passing through the extrapolated point(s)) tomore closely match the actual border of the vascular object. In doingso, the active-contour application may consider, or take into account atleast (i) image gradients (i.e., gradient factor), (ii) the proximity ofthe border to each extrapolated point (i.e., continuity or control-pointfactor), and/or (iii) border curvature or smoothness (i.e., curvature orboundary factor). Specifically, the gradient factor can be used toadjust the border if the neighboring pixels (as opposed to the pixels ofthe border) include border characteristics (e.g., a dark-to-lighttransition, etc.). In other words, if the neighboring pixels includeborder-like characteristics (or at least more so than the pixels formingthe border), then the border is adjusted. The continuity factor and thecurvature factor can be used to ensure that the border passes througheach extrapolated point and does not include any sharp transitions(e.g., corners, etc.), respectively. In one embodiment of the presentinvention, the active-contour application is further adapted to adjustrelated borders on adjacent images if the boarder is manually adjusted.

A more complete understanding of the system and method of identifying aborder on an IVUS image will be afforded to those skilled in the art, aswell as a realization of additional advantages and objects thereof, by aconsideration of the following detailed description of the preferredembodiment. Reference will be made to the appended sheets of drawingswhich will first be described briefly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a vascular-border-identification system in accordancewith one embodiment of the present invention.

FIG. 2 illustrates and exemplary intra-vascular ultrasound (IVUS) image.

FIG. 3 illustrates a plurality of borders that can be identified in anIVUS image.

FIG. 4 illustrates a plurality of control points on one of the bordersdepicted in FIG. 3.

FIG. 5 illustrates how a plurality of 2D vascular images can be used togenerate a 3D vascular image.

FIG. 6 illustrates how the control points from a first image (e.g., theimage depicted in FIG. 4) can be extrapolated onto a second image.

FIG. 7 illustrates a vascular image including a luminal boundary, amedial-adventitial boundary, and a plaque component locatedtherebetween.

FIG. 8 illustrates a method of identifying a border of a vascular objectin accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a system and method of using a firstvascular image, or more particularly a plurality of control pointslocated thereon, to identify a border on a second vascular image. In thedetailed description that follows, like element numerals are used todescribe like elements illustrated in one or more figures.

Embodiments of the present invention operate in accordance with anintra-vascular ultrasound (IVUS) device and a computing deviceelectrically connected thereto. FIG. 1 illustrates avascular-border-identification system 10 in accordance with oneembodiment of the present invention. Specifically, an IVUS console 110is electrically connected to a computing device 120 and a transducer 114via a catheter 112. The transducer 114 is inserted into a blood vesselof a patient (not shown) and used to gather IVUS data (i.e.,blood-vessel data, or data that can be used to identify the shape of ablood vessel, its density, its composition, etc.). The IVUS data is thenprovided to (or acquired by) the IVUS console 110, where it is used toproduce an IVUS image of the vessel.

More particularly, IVUS data is typically gathered in segments, eitherthrough a rotating transducer or an array of circumferentiallypositioned transducers, where each segment represents an angular portionof an IVUS image. Thus, it takes a plurality of segments (or a set ofIVUS data) to image an entire cross-section of a vascular object.Furthermore, multiple sets of IVUS data are typically gathered frommultiple locations within a vascular object (e.g., by moving thetransducer linearly through the vessel). These multiple sets of data canthen be used to create a plurality of two-dimensional (2D) images or onethree-dimensional (3D) image. It should be appreciated that the presentinvention is not limited to the use of an IVUS device (or theacquisition of IVUS data), and may further include using thermographicdevices, optical devices (e.g., an optical coherence tomography (OCT)console), MRI devices, or any vascular imaging devices generally knownto those skilled in the art. It should further be appreciated that thecomputing device depicted in FIG. 1 includes, but its not limited to,personal computers or any other data-processing devices (general purposeor application specific) that are generally known to those skilled inthe art.

The IVUS data (or multiple sets thereof) is then provided to (oracquired by) the computing device 120. In one embodiment of the presentinvention, the computing device 120 includes a plurality of applicationsoperating thereon—i.e., a border-detection application 122, anextrapolation application 124, and an active-contour application 126.These applications are used to (i) identify a border and control pointson a first IVUS image (i.e., any IVUS image), (ii) extrapolate thecontrol points to a second IVUS image (i.e., another IVUS image), (iii)identify a border on the second IVUS image, and (iv) adjust the borderon the second IVUS image. It should be appreciated that the numberand/or location of the applications depicted in FIG. 1 are not intendedto limit the present invention, but are merely provided to illustratethe environment in which the present invention operates. Thus, forexample, using a single application to perform the applicationfunctions, as discussed herein, or remotely locating at least one of theapplications (in whole or in part) is within the spirit and scope of thepresent invention. It should further be appreciated that, while thepresent invention is discussed in terms of singularities (e.g.,identifying a border on one IVUS image, extrapolating control points toanother IVUS image, etc.), the present invention is not so limited. Infact, the present invention is particularly useful if it is used on aplurality of IVUS images (e.g., identifying borders on every fifth IVUSimage, extrapolating control points from the fifth IVUS image to thenext four IVUS images, etc.). It should also be appreciated that theterms “first” and “second,” as those terms are used herein, are usedbroadly to identify any two IVUS images. Thus, the phrase “second IVUSimage” may be used to identify an IVUS image distinct from a first IVUSimage (as opposed to the second IVUS image in a series of IVUS images).

Vascular objects include several identifiable borders. For example, theluminal border demarcates the blood-intima interface and themedial-adventitial border demarcates the external elastic membrane (theboundary between the media and adventitia). By identifying theseborders, the plaque-media complex, which is located there between, canbe analyzed and/or calculated. It should be appreciated that the presentinvention is not limited to the identification of any particular border,and includes all vascular boundaries generally known to those skilled inthe art.

Referring back to FIG. 1, the border-detection application 122 isadapted to identify a border on a vascular image (e.g., an IVUS image).In one embodiment of the present invention, this is performed byanalyzing the IVUS image, or IVUS data that corresponds the IVUS image,to determine certain gradients located therein. This is because bordersof vascular objects can be identified by a change in pixel color (e.g.,light-to-dark, dark-to-light, shade1-to-shade2, etc).

For example, FIG. 2 illustrates an exemplary IVUS image 20 of a vascularobject. Starting from the center and working outward, the catheter canbe identified by the first light-to-dark transition (or gradient). Thecatheter border is further identified in FIG. 3 (i.e., 330). Referringback to FIG. 2, and continuing outward, the next dark-to-lighttransition (or gradient) identifies the luminal border (i.e., see FIG.3, 320). The medial-adventitial border can then be identified by goingoutward from the luminal border until the next dark-to-light transition(or gradient) is found (see FIG. 3, 310). It should be appreciated thatbecause the IVUS image is constructed using gray-scales, it may benecessary to utilize an algorithm and/or at least one threshold value toidentify precisely where the image changes from light to dark (or viceversa). However, it should further be appreciated that the presentinvention is not limited to any particular algorithm for identifying theaforementioned transitions, and includes all algorithms (and/orthreshold values) generally known to those skilled in the art.

Once the border is identified, the border-detection algorithm is furtheradapted to identify at least one control point on the border. Forexample, with reference to FIGS. 3 and 4, the border-detection algorithmcan be used to identify a plurality of control points 22 on the luminalborder 320. It should be appreciated that the location and number ofcontrol points depicted in FIG. 4 are not intended to limit the presentinvention, and are merely provided to illustrate the environment inwhich the present invention may operate. In an alternate embodiment, theborder-detection application 122 is adapted to identify a border usinguser-identified control points. Such an embodiment is discussed indetail in U.S. Pat. No. 6,381,350, which issued Apr. 30, 2002, and isincorporated herein, in its entirety, by reference.

Referring back to FIG. 1, once the border and control point(s) areidentified on a first vascular image, the extrapolation application 124is used to identify at least one control point on at least one otherIVUS image. In a preferred embodiment of the present invention, this isdone by extrapolating the previously identified control points to atleast one other IVUS image. By doing this, multiple 2D images (or atleast one 3D image) can be produced. For example, as illustrated in FIG.5, multiple 2D images (e.g., 20, 52 a-52 d, etc.) are used to produce a3D image of a tubular (e.g., vascular) object 50.

FIG. 6 illustrates how an identified control point can be extrapolatedto another IVUS image. Specifically, the control points that wereillustrated in FIG. 4 (i.e., 22) are extrapolated (or copied) to anotherIVUS image (e.g., 52 d), thus creating a second set of control points62. In one embodiment of the present invention, the control points areextrapolated using Cartesian coordinates. It should be appreciated that,while FIG. 6 illustrates control points being extrapolated to anadjacent image, the present invention is not so limited. Thus,extracting control points to additional images (e.g., 52 c, 52 b, etc.)is within the spirit and scope of the present invention.

Once the control points are extrapolated, the extrapolating applicationis further adapted to identify (or approximate) a border based on theextrapolated points. For example, as shown in FIG. 6, the extrapolatedpoints 62 may be connected using a plurality of lines 64, where thelines are either straight or curved (not shown). In another embodimentof the present invention, the extrapolating application is adapted touse an algorithm (e.g., a cubic-interpolation algorithm, etc.) toidentify line shape.

Referring back to FIG. 1, the active-contour application 126 is thenused to adjust the border to more closely match the actual border of thevascular object. In doing so, the active-contour application 126 mayconsider or take into account at least (i) image gradients (i.e.,gradient data), (ii) the proximity of the border to each extrapolatedpoint (i.e., continuity or control-point factor), and/or (iii) bordercurvature or smoothness (i.e., curvature or boundary factor).Specifically, by considering gradient data (or a gradient factor), theborder can be adjusted if the neighboring pixels (as opposed to thepixels of the border) include border characteristics (e.g., adark-to-light transition, etc.). By considering a continuity orcontrol-point factor, the border can be adjusted so that it passesthrough each extrapolated point. Furthermore, by considering a curvatureor boundary factor, the border can be adjusted to prevent sharptransitions (e.g., corners, etc.). In one embodiment of the presentinvention, the continuity and curvature factors are also used to connectrelated borders on adjacent images. It should be appreciated that ifmultiple factors are being considered, then individual factors may beweighted more heavily than others. This becomes important if the factorsproduce different results (e.g., the gradient factor suggests adjustingthe border away from an extrapolated point, etc.). It should further beappreciated that the active-contour application may also be used toadjust the border identified by the border-detection application. Itshould also be appreciated that the present invention is not limited tothe use of the aforementioned factors for border optimization, and thatthe use of additional factors (e.g., frequency factor, etc.) to adjust(or optimize) a border is within the spirit and scope of the presentinvention.

In one embodiment of the present invention, the adjusted borders areconfigured to be manually manipulated. In other words, at least onepoint on the border can be selected and manually moved to a newlocation. The active-contour application is then used (as previouslydiscussed) to reconstruct the border accordingly. In another embodimentof the present invention, the active-contour application is furtheradapted to adjust related borders in adjacent images. This is done byfitting a geometrical model (e.g., a tensor product B-spline, etc.) overthe surface of a plurality of related borders (e.g., as identified onmultiple IVUS images). A plurality of points on the geometrical modelare then parameterized and formulated into a constrained least-squaressystem of equations. If a point on the border is manually moved, theactive-contour application can utilize these equations to calculate aresulting surface (or mesh of control points). The affected borders(e.g., adjacent borders) can then be adjusted accordingly.

Once the border has been sufficiently adjusted, the aforementionedprocess can be repeated to identify additional borders. In an alternateembodiment of the present invention, multiple borders (e.g., luminal andmedial-adventitial borders) are identified concurrently. The multipleborder can then be imaged (in either 2D or 3D) and analyzed by either askilled practitioner or a computer algorithm. For example, asillustrated in FIG. 7, the luminal border 74 and the medial-adventitialborder 76 can be used (by either a clinician or an algorithm) toidentify the plaque-media complex 78 of a vascular object.

One method of identify a border on a vascular image is illustrated inFIG. 8. Specifically, in step 810, multiple sets of IVUS data areacquired, where each set of IVUS data corresponds to a 2D IVUS image. Atstep 812, a border is approximated in one IVUS image (e.g., usinggradient data, etc.). Control points on the approximated border are thenidentified at step 814. At step 816, these control points are then usedto identify additional control points on additional 2D IVUS images(e.g., via extrapolation, etc.). These additional control points arethen used to approximate at least one other border at step 818, which isthen adjusted at step 820. In one embodiment, the border is adjusted inaccordance with at least gradient data.

Having thus described a preferred embodiment of a system and method ofidentifying a border on a vascular image, it should be apparent to thoseskilled in the art that certain advantages of the system have beenachieved. It should also be appreciated that various modifications,adaptations, and alternative embodiments thereof may be made within thescope and spirit of the present invention. The invention is furtherdefined by the following claims.

1-20. (canceled)
 21. A method of identifying a border of a vascularobject, comprising: acquiring multiple sets of blood-vessel data relatedto a vascular object, each set of blood-vessel data corresponding to animage of at least a portion of the vascular object; using a first set ofblood-vessel data to approximate a border on a first image of thevascular object; identifying at least one control point on the border onthe first image; extrapolating the at least one identified control pointto a second set of blood-vessel data to define at least one othercontrol point on a second image; using the at least one other controlpoint to approximate at least one other border on the second image; andadjusting a position of the at least one other border on the secondimage in accordance with at least one factor selected from the group offactors consisting of: a gradient factor, a continuity factor, and acurvature factor.
 22. The method of claim 21, wherein the step ofacquiring multiple sets of blood-vessel data comprises acquiringmultiple sets of intra-vascular ultrasound (IVUS) data, where each setcorresponds to an IVUS image of the vascular object.
 23. The method ofclaim 21, wherein the step of using the first set of blood-vessel datato approximate a border on the first image comprises identifyinggradients in the first image and using the identified gradients toapproximate the border on the first image of the vascular object. 24.The method of claim 21, wherein the second set of blood-vessel data isan adjacent the first set of blood-vessel data such that the secondimage is an image adjacent the first image.
 25. The method of claim 21,wherein the step adjusting the position of the at least one other bordercomprises adjusting the position of the at least one other border inaccordance with at least two factors selected from the group of factorsconsisting of: a gradient factor, a continuity factor, and a curvaturefactor.
 26. The method of claim 25, wherein one of the at least twofactors is weighted more heavily than another of the at least twofactors.
 27. The method of claim 21, wherein the step of adjusting theposition of the at least one other border comprises adjusting the atleast one other border in accordance with a continuity factor, thecontinuity factor representing an amount of continuity between adjacentcontrol points on the at least one other border on the second image. 28.The method of claim 21, wherein the step of adjusting the position ofthe at least one other border comprises adjusting the at least one otherborder in accordance with a curvature factor, the curvature factorrepresenting an amount of continuity between adjacent portions of the atleast one other border.
 29. The method of claim 21, further comprising:adjusting the position of the at least one other border on the secondimage in response to an adjustment in the position of the border on thefirst image.
 30. The method of claim 29, wherein the step of adjustingthe position of the at least one other border on the second image inresponse to the adjustment in the position of the border on the firstimage is performed automatically.
 31. The method of claim 30, whereinthe position of the border on the first image is adjusted manually by auser.
 32. A border-identification system comprising: a computing deviceadapted to acquire multiple sets of blood-vessel data related to avascular object, each set of blood vessel data corresponding to an imageof at least a portion of the vascular object; a border-detectionapplication operating on the computing device, the border-detectionapplication configured to: approximate a border on a first image of thevascular object using a first set of blood-vessel data; identify atleast one control point on the border on the first image; extrapolatethe at least one identified control point to a second set ofblood-vessel data to define at least one other control point on a secondimage; approximate at least one other border on the second image usingthe at least one other control point; and adjust a position of the atleast one other border on the second image in accordance with at leastone factor selected from the group of factors consisting of: a gradientfactor, a continuity factor, and a curvature factor
 33. Theborder-identification system of claim 32, wherein the computing deviceis configured to be in communication with a data-gathering device toacquire the multiple sets of blood-vessel data.
 34. Theborder-identification system of claim 33, wherein the data-gatheringdevice is configured to generate the multiple sets of blood-vessel data.35. The border-identification system of claim 34, wherein thedata-gathering device comprises an intra-vascular ultrasound (IVUS)system.
 36. The border-identification system of claim 32, wherein theborder detection application is configured to adjust the position of theat least one other border on the second image with at least two factorsselected from the group of factors consisting of: a gradient factor, acontinuity factor, and a curvature factor.
 37. The border-identificationsystem of claim 36, wherein one of the at least two factors is weightedmore heavily than another of the at least two factors.
 38. Theborder-identification system of claim 32, wherein the border detectionapplication is configured to adjust the position of the at least oneother border on the second image in response to an adjustment in theposition of the border on the first image.
 39. The border-identificationsystem of claim 38, wherein the border detection application isconfigured to automatically adjust the position of the at least oneother border on the second image in response to the adjustment in theposition of the border on the first image.
 40. The border-identificationsystem of claim 39, wherein the border detection application isconfigured to automatically adjust the position of the at least oneother border on the second image in response to a manual adjustment inthe position of the border on the first image.